Additives for oil compositions

ABSTRACT

Specific polymers of ethylene and different unsaturated esters provide oils with improved low temperature flow properties.

This invention relates to oil compositions, primarily to fuel oil compositions, and more especially to fuel oil compositions susceptible to wax formation at low temperatures, to copolymers for use with such fuel oil compositions, and to methods for their manufacture.

Fuel oils, whether derived from petroleum or from vegetable sources, contain components, e.g., alkanes, that at low temperature tend to precipitate as large crystals or spherulites of wax in such a way as to form a gel structure which causes the fuel to lose its ability to flow. The lowest temperature at which the fuel will still flow is known as the pour point.

As the temperature of the fuel falls and approaches the pour point, difficulties arise in transporting the fuel through lines and pumps. Further, the wax crystals tend to plug fuel lines, screens, and filters at temperatures above the pour point. These problems are well recognised in the art, and various additives have been proposed, many of which are in commercial use, for depressing the pour point of fuel oils. Similarly, other additives have been proposed and are in commercial use for reducing the size and changing the shape of the wax crystals that do form. Smaller size crystals are desirable since they are less likely to clog a filter. The wax from a diesel fuel, which is primarily an alkane wax, crystallizes as platelets; certain additives inhibit this and cause the wax to adopt an acicular habit, the resulting needles being more likely to pass through a filter than are platelets. The additives may also have the effect of retaining in suspension in the fuel the crystals that have formed, the resulting reduced settling also assisting in prevention of blockages.

Effective wax crystal modification (as measured by cold filter plugging point (CFPP) and other operability tests, as well as simulated and field performance) may be achieved by ethylene-vinyl acetate (EVAC) or propionate copolymer-based flow improvers. British Specification No. 1,086,036, EP-A-527,322 and EP-A-518,406 describe terpolymers suitable as latices for coatings, these terpolymers being formed by copolymerizing ethylene with a vinyl ester of a tertiary or quaternary aliphatic carboxylic acid and a further ester monomer which may be vinyl acetate.

British Specification No. 1,314,855 describes terpolymers of ethylene, vinyl acetate and a vinyl ester of a long-chain carboxylic acid which may be a saturated carboxylic acid having 8 to 30 carbon atoms. The only branched-chain carboxylic acid specifically disclosed is isostearic acid (C₁₈). These terpolymers are described as useful in lubricating oils as viscosity index improvers.

British Specification No. 1,244,512 describes terpolymers of ethylene, a vinyl ester of a C₂ to C₄ monocarboxylic acid and an unsaturated ester having a C₁₀ to C₂₂ alkyl group, and preferably of the formula. ##STR1##

Wherein X is hydrogen or a methyl group, and Y is a OOCR or -COOR wherein R is preferably a C₁₀ to C₁₆ straight chain or branched chain alkyl group. All the specifically disclosed esters wherein Y is OOCR have straight chain alkyl groups.

WO 96/07718 discloses oil soluble ethylene terpolymers containing ethylene units and different vinyl ester units, and their use as additives for improving the low temperature flow properties of fuel oil compositions. Polymer examples 1 to 4 inclusive on page 19 (Table 1) are ethylene-vinyl acetate-vinyl 2-ethyl hexanoate terpolymers having various proportions of the two unsaturated esters, as well as differing number average molecular weights and branching characteristics.

The polymers of WO 96/07718 are effective low temperature flow improvers and have the advantage of being manufactured from commercially available vinyl ester monomers. However, there is a continual need in the art to produce more effective polymers giving improved performance. Surprisingly, it has now been found that certain detailed characteristics of the polymer structure may be controlled to provide more effective additives.

In a first aspect therefore, this invention provides an additive composition comprising an oil soluble ethylene polymer comprising, in addition to units derived from ethylene, units of the formula: ##STR2## and units of the formula: ##STR3## wherein each R¹ and R² group independently represents hydrogen or methyl; each R³ group independently represents an alkyl group having between 1 and 4 carbon atoms; each R⁴ group independently represents a branched chain alkyl group having up to 15 carbon atoms and different from R³ ;

characterised in that:

(i) the mole percentage of units (I) in the polymer is in the range of 2.5 to 4.5%,

(ii) the mole percentage of units (II) in the polymer is in the range of 9.5 to 14%,

(iii) the total mole percentage of units (I) and units (II) in the polymer is in the range of 12 to 18%,

(iv) the number average molecular weight (Mn) of the polymer is in the range of 3500 to 6000, and

(v) the degree of branching of the polymer is in the range of 2.2 to 3.6 methyl groups per 100 methylene units, as measured by proton NMR and corrected for the number of methyl and methylene groups in R³ and R⁴ groups.

In a second aspect, this invention provides an additive concentrate composition comprising the additive of the first aspect and a mutually-compatible solvent thereof.

In a third aspect, this invention provides an oil composition comprising an oil and a minor amount of the composition of the first or second aspect.

In a fourth aspect, this invention provides the polymer defined under the first aspect.

In a fifth aspect, this invention provides the use of the polymer of the fourth aspect, or of the composition of the first or second aspects, to improve the low temperature flow properties of an oil.

In the sixth aspect, this invention provides a method for improving the low temperature properties of an oil, comprising admixture of the oil with the composition of the first or second aspects, or the polymer of the fourth aspect.

The polymers defined under this invention prove highly effective in comparison to analogous polymers not having all of the features (i) to (v) recited above.

BRIEF DESCRIPTION OF THE DRAWINGS

The Figure is a proton NMR spectrum for an ethylene-vinyl acetate vinyl-2-ethylexanoate polymer.

The Additive Composition (first aspect of the invention)

The Polymer

In the polymer, R⁴ preferably represents a branched chain alkyl group having 8 to 15 carbon atoms other than a tertiary alkyl group, or R⁴ more preferably represents a branched chain alkyl group having at most seven carbon atoms.

In units of the formula I, R¹ advantageously represents hydrogen, and R³ advantageously represents ethyl or, especially, methyl. Advantageously R³ is not t-butyl, but otherwise may be straight-chain or branched, although it is preferred that R³ is a primary or secondary alkyl group. In units of the formula II, R² advantageously represents hydrogen. Advantageously, when R⁴ represents a branched chain alkyl group having at most 7 carbon atoms, it is not a tertiary alkyl group.

Advantageously, R¹ and R² are both hydrogen.

R⁴ preferably represents a secondary alkyl group, such as isopropyl, isobutyl, secbutyl, isopentyl, neo-pentyl, 1- and 2-methyl butyl, 1,2-dimethyl and 1-ethyl propyl, isohexyl, 1-, 2- and 3-methyl pentyl, 1- and 2-ethyl hexyl, 1- and 2-methyl heptyl, 1-ethyl propyl and, especially, 1-ethyl pentyl being preferred.

Polymers wherein R³ represents a primary or secondary alkyl group, and R⁴ represents a secondary alkyl group are particularly preferred.

Preferably, R¹ and R² each represent hydrogen and R³ represents a primary alkyl group.

The polymer has at least three different repeat monomer units, i.e., is derivable from at least three different monomers, and includes polymers derivable from four or more monomers. For example, the polymer may contain two or more different units of the formula I or II, and/or may contain units of the formula ##STR4## wherein R⁵ represents a hydrocarbyl group having 5 or more carbon atoms other than one as defined by R⁴ .

As used in this specification the term "hydrocarbyl" refers to a group having a carbon atom directly attached to the rest of the molecule and having a hydrocarbon or predominantly hydrocarbon character. Among these, there may be mentioned hydrocarbon groups, including aliphatic, (e.g., alkyl), alicyclic (e.g., cycloalkyl), aromatic, aliphatic and alicyclic-substituted aromatic, and aromatic-substituted aliphatic and alicyclic groups. Aliphatic groups are advantageously saturated. These groups may contain non-hydrocarbon substituents provided their presence does not alter the predominantly hydrocarbon character of the group. Examples include keto, halo, hydroxy, nitro, cyano, alkoxy and acyl. If the hydrocarbyl group is substituted, a single (mono) substituent is preferred. Examples of substituted hydrocarbyl groups include 2-hydroxyethyl, 3-hydroxypropyl, 4-hydroxybutyl, 2-ketopropyl, ethoxyethyl, and propoxypropyl. The groups may also or alternatively contain atoms other than carbon in a chain or ring otherwise composed of carbon atoms. Suitable hetero atoms include, for example, nitrogen, sulphur, and, preferably, oxygen. Advantageously, the hydrocarbyl group contains at most 30, preferably at most 15, more preferably at most 10 and most preferably at most 8, carbon atoms.

The polymer may also contain units of formulae other than those mentioned above, for example units of the formula

    -CH.sub.2 --CHR.sup.6 -                                    IV

where R⁶ represents -OH, or of the formula

    -CCH.sub.3 (CH.sub.2 R.sup.7)-CHR.sup.8 -                  V

where R⁷ and R⁸ each independently represent hydrogen or an alkyl group with up to 4 carbon atoms, the units V advantageously being derived from isobutylene, 2-methylbut-2-ene or 2-methylpent-2-ene.

As indicated above, the polymer may contain a mixture of different species of R³ and/or R⁴. It is also within the scope of the invention to provide a composition comprising a mixture of two or more polymers according to the first aspect of the invention.

The features (i) to (v) inclusive of the polymer provide an optimal polymer structure highly effective at improving low temperature flow of oils. In particular, polymers wherein;

(i) is in the range of 3 to 4.1, preferably from 3.1 to 3.9;

(ii) is in the range of 10.1 to 13, preferably from 10.4 to 12.5;

(iii) is in the range of 13.8 to 17, preferably from 14.2 to 15.4; and

(v) is in the range of 2.2 to 3.4 preferably from 2.2 to 3.3

have been found to give particularly good flow improvement.

Preferably, (iv) is in the range of 4000 to 6000; more preferably 4100 to 6000. Mn in this specification refers to that value measured by GPC, in comparison to polystyrene standards.

The polymer is especially useful in fuel oils having a relatively high wax content, e.g., a wax content of 2.5 to 4.5 % by weight per weight of fuel, preferably 3.0 to 4.5, such as 3.5 to 4.5% wt. measured at 10° C. below wax appearance temperature (WAT).

The polymer should preferably be soluble in the oil to the extent of at least 1000 ppm by weight per weight of oil at ambient temperature. However, at least some of the terpolymer may come out of solution near the cloud point of the oil and function to modify the wax crystals that form.

An important feature of the polymer is its degree of branching, in the sense of the relatively small proportion of alkyl branches from the main polymer chain. This degree of branching may be expressed in terms of the number of methyl groups per 100 methylene units, as measured by proton NMR, which is, as indicated above, in the range of 2.2 to 3.6.

In calculating this linearity, the proportion of CH₃ groups per 100 methylene groups is measured by proton NMR and corrected for the number of methyl and methylene groups in the alkyl groups of R³ and R⁴ of the carboxylate side chains.

By way of exemplification, FIG. 1 shows a sample proton NMR spectrum for an ethylene-vinyl acetate vinyl-2-ethylhexanoate polymer.

As exemplified in FIG. 1, the peaks relevant to the calculation are annotated b, c, d, and e, wherein b originates for the hydrogen(s) on the carbon atom situated α to the carbonyl group on the carboxylate side chain R⁴ (in this example, a methine carbon); c represents the equivalent hydrogen(s) on R³ (in this example, methyl); d originates from the hydrogens of the methylenes and methines of the polymer main chain and carboxylate side chains, other than the main chain methine from which the carboxylate side chain depends when R¹ and/or R² in formula 1 represent H; and e originates from the hydrogens of the methyls of the polymer main chain and carboxylate side chains.

Representing the area under each of the peaks b, c, d and e as B, C, D and E respectively, the number of CH₃ units per 100 methylene groups, corrected for carboxylate side chain methyl and methylene groups, is calculated as: ##EQU1## to give the degree of branching of the terpolymer.

The polymer may be made by any of the methods known in the art, e.g., by solution polymerization with free radical initiation, or by high pressure polymerization, conveniently carried out in an autoclave or a tubular reactor.

Advantageously, polymerization is effected in the presence of an initiator and if desired or required a molecular weight regulator at elevated pressure, e.g., between 90 and 125 bar (9 and 12.5 MPa) and elevated temperature, but preferably below about 130° C., for example within the range of from 90° C. to 125° C. Maintaining a temperature below the above-mentioned limit enables a polymer having the desired linearity to be obtained; other means of controlling linearity, as known in the art, may also be used.

The Additive Composition

The additive may contain other additives for improving low temperature and/or other properties, many of which are in use in the art or known from the literature.

For example, the composition may also contain (A) a further ethylene-unsaturated ester, especially a vinyl ester, copolymer. As disclosed in U.S. Pat. No. 3961916, flow improver compositions may comprise a wax growth arrestor and a nucleating agent.

The combination of the polymer and the copolymer may provide surprisingly improved benefits in performance. The present invention accordingly also provides the additive composition of the first aspect additionally comprising one or more ethylene-unsaturated, especially vinyl, ester copolymers different from the polymer defined under the first aspect; and further provides an additive composition comprising the polymer as defined under the first aspect and one or more copolymers different from the polymer. Advantageously, the polymer and the copolymer will differ in molar ester proportion and number average molecular weight, the higher ester proportion preferably corresponding to the lower molecular weight.

The additive composition may also comprise additional cold flow improvers, including (B) a comb polymer.

Comb polymers (B) are polymers in which branches containing hydrocarbyl groups are pendant from a polymer backbone, and are discussed in "Comb-Like Polymers. Structure and Properties", N. A. Plate and V. P. Shibaev, J. Poly. Sci. Macromolecular Revs., 8, p 117 to 253 (1974).

Generally, comb polymers have one or more long chain hydrocarbyl branches, e.g., oxyhydrocarbyl branches, normally having from 10 to 30 carbon atoms, pendant from a polymer backbone, said branches being bonded directly or indirectly to the backbone. Examples of indirect bonding include bonding via interposed atoms or groups, which bonding can include covalent and/or electrovalent bonding such as in a salt.

Advantageously, the comb polymer is a homopolymer or a copolymer having at least 25 and preferably at least 40, more preferably at least 50, molar per cent of the units of which have, side chains containing at least 6, and preferably at least 10, atoms.

As examples of preferred comb polymers there may be mentioned those of the general formula ##STR5## wherein D =R¹¹, COOR¹¹, OCOR¹¹, R¹² COOR¹¹, or OR¹¹,

E =H, CH₃, D, or R¹²,

G =H or D

J =H, R¹², R¹² COOR¹¹, or an aryl or heterocyclic group,

K =H, COOR¹², OCOR¹², OR¹² or COOH,

L =H, R¹², COOR ¹², OCOR¹², COOH, or aryl,

R¹¹ >C₁₀ hydrocarbyl,

R¹² >C₁ hydrocarbyl or hydrocarbylene,

and m and n represent mole fractions, m being finite and preferably within the range of from 1.0 to 0.4, n being less than 1 and preferably in the range of from 0 to 0.6. R¹¹ advantageously represents a hydrocarbyl group with from 10 to 30 carbon atoms, while R¹² advantageously represents a hydrocarbyl or hydrocarbylene group with from 1 to 30 carbon atoms.

The comb polymer may contain units derived from other monomers if desired or required.

These comb polymers may be copolymers of maleic anhydride or fumaric or itaconic acids and another ethylenically unsaturated monomer, e.g., an α-olefin, including styrene, or an unsaturated ester, for example, vinyl acetate or homopolymer of fumaric or itaconic acids. It is preferred but not essential that equimolar amounts of the comonomers be used although molar proportions in the range of 2 to 1 and 1 to 2 are suitable. Examples of olefins that may be copolymerized with e.g., maleic anhydride, include 1-decene, 1-dodecene, 1 -tetradecene, 1 -hexadecene, and 1 -octadecene.

The acid or anhydride group of the comb polymer may be esterified by any suitable technique and although preferred it is not essential that the maleic anhydride or fumaric acid be at least 50% esterified. Examples of alcohols which may be used include n-decan-1-ol, n-dodecan-l-ol, n-tetradecan-1-ol, n-hexadecan-1-ol, and n-octadecan-1-ol. The alcohols may also include up to one methyl branch per chain, for example, 1-methylpentadecanl-ol or 2-methyltridecan-l-ol. The alcohol may be a mixture of normal and single methyl branched alcohols. It is preferred to use pure alcohols rather than the commercially available alcohol mixtures but if mixtures are used the R¹² refers to the average number of carbon atoms in the alkyl group; if alcohols that contain a branch at the 1 or 2 positions are used R¹² refers to the straight chain backbone segment of the alcohol.

These comb polymers may especially be fumarate or itaconate polymers and copolymers such for example as those described in EP-A-153176, -153177 and -225688, and WO 91/16407.

Particularly preferred fumarate comb polymers are copolymers of alkyl fumarates and vinyl acetate, in which the alkyl groups have from 12 to 20 carbon atoms, more especially polymers in which the alkyl groups have 14 carbon atoms or in which the alkyl groups are a mixture of C₁₄ /C₁₆ alkyl groups, made, for example, by solution copolymerizing an equimolar mixture of fumaric acid and vinyl acetate and reacting the resulting copolymer with the alcohol or mixture of alcohols, which are preferably straight chain alcohols. When the mixture is used it is advantageously a 1:1 by weight mixture of normal C₁₄ and C₁₆ alcohols. Furthermore, mixtures of the C14 ester with the mixed C₁₄ /C₁₆ ester may advantageously be used. In such mixtures, the ratio of C₁₄ to C₁₄ /C₁₆ is advantageously in the range of from 1:1 to 4:1, preferably 2:1 to 7:2, and most preferably about 3:1, by weight. The particularly preferred comb polymers are those having a number average molecular weight, as measured by vapour phase osmometry, of 1,000 to 100,000, more especially 1,000 to 30,000.

Other suitable comb polymers are the polymers and copolymers of α-olefins and esterified copolymers of styrene and maleic anhydride, and esterified copolymers of styrene and fumaric acid; mixtures of two or more comb polymers may be used in accordance with the invention and, as indicated above, such use may be advantageous. Other examples of comb polymers are hydrocarbon polymers, e.g., copolymers of ethylene and at least one α-olefin, the α-olefin preferably having at most 20 carbon atoms, examples being n-decene-1 and n-dodecene-1. Preferably, the number average molecular weight of such a copolymer is at least 30,000 measured by GPC. The hydrocarbon copolymers may be prepared by methods known in the art, for example using a Ziegler type catalyst.

Other additives for improving low temperature properties are:

(C) Polar nitrogen compounds. Such compounds are oil-soluble polar nitrogen compounds carrying one or more, preferably two or more, substituents of the formula >NR¹³, where R¹³ represents a hydrocarbyl group containing 8 to 40 atoms, which substituent or one or more of which substituents may be in the form of a cation derived therefrom. The oil soluble polar nitrogen compound is generally one capable of acting as a wax crystal growth inhibitor in fuels, it comprises for example one or more of the following compounds:

An amine salt and/or amide formed by reacting at least one molar proportion of a hydrocarbyl-substituted amine with a molar proportion of a hydrocarbyl acid having from 1 to 4 carboxylic acid groups or its anhydride, the substituent(s) of formula >NR¹³ being of the formula -NR¹³ R¹⁴ where R¹³ is defined as above and R¹⁴ represents hydrogen or R¹³, provided that R¹³ and R¹⁴ may be the same or different, said substituents constituting part of the amine salt and/or amide groups of the compound.

Ester/amides may be used, containing 30 to 300, preferably 50 to 150, total carbon atoms. These nitrogen compounds are described in U.S. Pat. No. 4 211 534. Suitable amines are predominantly C₁₂ to C₄₀ primary, secondary, tertiary or quaternary amines or mixtures thereof but shorter chain amines may be used provided the resulting nitrogen compound is oil soluble, normally containing about 30 to 300 total carbon atoms. The nitrogen compound preferably contains at least one straight chain C₈ to C₄₀, preferably C₁₄ to C₂₄, alkyl segment.

Suitable amines include primary, secondary, tertiary or quaternary, but are preferably secondary. Tertiary and quaternary amines only form amine salts. Examples of amines include tetradecylamine, cocoamine, and hydrogenated tallow amine. Examples of secondary amines include dioctadecyl amine and methylbehenyl amine. Amine mixtures are also suitable such as those derived from natural materials. A preferred amine is a secondary hydrogenated tallow amine, the alkyl groups of which are derived from hydrogenated tallow fat composed of approximately 4% C₁₄, 31% C₁₆, and 59% C₁₈.

Examples of suitable carboxylic acids and their anhydrides for preparing the nitrogen compounds include ethylenediamine tetraacetic acid, and carboxylic acids based on cyclic skeletons, e.g., cyclohexane-1,2-dicarboxylic acid, cyclohexene-1,2-dicarboxylic acid, cyclopentane-1,2-dicarboxylic acid and naphthalene dicarboxylic acid, and 1,4-dicarboxylic acids including dialkyl spirobislactones. Generally, these acids have about 5 to 13 carbon atoms in the cyclic moiety. Preferred acids useful in the present invention are benzene dicarboxylic acids e.g., phthalic acid, isophthalic acid, and terephthalic acid. Phthalic acid and its anhydride are particularly preferred. The particularly preferred compound is the amide-amine salt formed by reacting 1 molar portion of phthalic anhydride with 2 molar portions of dihydrogenated tallow amine. Another preferred compound is the diamide formed by dehydrating this amide-amine salt.

Other examples are long chain alkyl or alkylene substituted dicarboxylic acid derivatives such as amine salts of monoamides of substituted succinic acids, examples of which are known in the art and described in U.S. Pat. No. 4 147 520, for example. Suitable amines may be those described above.

Other examples are condensates, for example, those described in EP-A-327427.

(D) A compound containing a cyclic ring system carrying at least two substituents of the general formula below on the ring system

    -A--NR.sup.15 R.sup.16

where A is a linear or branched chain aliphatic hydrocarbylene group optionally interrupted by one or more hetero atoms, and R¹⁵ and R¹⁶ are the same or different and each is independently a hydrocarbyl group containing 9 to 40 atoms optionally interrupted by one or more hetero atoms, the substituents being the same or different and the compound optionally being in the form of a salt thereof. Advantageously, A has from 1 to 20 carbon atoms and is preferably a methylene or polymethylene group. Such compounds are described in WO 93/04148.

(E) A hydrocarbon polymer. Examples of suitable hydrocarbon polymers are those of the general formula ##STR6## wherein T =H or R²¹ wherein

R²¹ =C₁ to C₄₀ hydrocarbyl, and

U =H, T, or aryl

and v and w represent mole fractions, v being within the range of from 1.0 to 0.0, w being in the range of from 0.0 to 1.0.

The hydrocarbon polymers may be made directly from monoethylenically unsaturated monomers or indirectly by hydrogenating polymers from polyunsaturated monomers, e.g., isoprene and butadiene.

Examples of hydrocarbon polymers are disclosed in WO 91/11488.

Preferred copolymers are ethylene α-olefin copolymers, having a number average molecular weight of at least 30,000. Preferably the c-olefin has at most 28 carbon atoms. Examples of such olefins are propylene, n-butene, isobutene, n-octene-1, isooctene-1, n-decene-1, and n-dodecene-1. The copolymer may also comprise small amounts, e.g., up to 10% by weight, of other copolymerizable monomers, for example olefins other than α-olefins, and non-conjugated dienes. The preferred copolymer is an ethylene-propylene copolymer.

The number average molecular weight of the ethylene cc-olefin copolymer is, as indicated above, preferably at least 30,000, as measured by gel permeation chromatography (GPC) relative to polystyrene standards, advantageously at least 60,000 and preferably at least 80,000. Functionally no upper limit arises but difficulties of mixing result from increased viscosity at molecular weights above about 150,000, and preferred molecular weight ranges are from 60,000 and 80,000 to 120,000.

Advantageously, the copolymer has a molar ethylene content between 50 and 85 per cent. More advantageously, the ethylene content is within the range of from 57 to 80%, and preferably it is in the range from 58 to 73%; more preferably from 62 to 71%, and most preferably 65 to 70%.

Preferred ethylene a-olefin copolymers are ethylene-propylene copolymers with a molar ethylene content of from 62 to 71% and a number average molecular weight in the range 60,000 to 120,000; especially preferred copolymers are ethylene-propylene copolymers with an ethylene content of from 62 to 71% and a molecular weight from 80,000 to 100,000.

The copolymers may be prepared by any of the methods known in the art, for example using a Ziegler type catalyst. The polymers should be substantially amorphous, since highly crystalline polymers are relatively insoluble in fuel oil at low temperatures.

Other suitable hydrocarbon polymers include a low molecular weight ethylene-α-olefin copolymer, advantageously with a number average molecular weight of at most 7,500, advantageously from 1,000 to 6,000, and preferably from 2,000 to 5,000, as measured by vapour phase osmometry. Appropriate α-olefins are as given above, or styrene, with propylene again being preferred. Advantageously the ethylene content is from 60 to 77 molar per cent, although for ethylene-propylene copolymers up to 86 molar per cent by weight ethylene may be employed with advantage.

The hydrocarbon polymer may most preferably be an oil-soluble hydrogenated block diene polymer, comprising at least one crystallizable block, obtainable by end-to-end polymerization of a linear diene, and at least one non-crystallizable block, the non-crystallizable block being obtainable by 1,2-configuration polymerization of a linear diene, by polymerization of a branched diene, or by a mixture of such polymerizations.

Advantageously, the block copolymer before hydrogenation comprises units derived from butadiene only, or from butadiene and at least one comonomer of the formula

    CH.sub.2 =CR.sup.1 -CR.sup.2 =CH.sub.2

wherein R¹ represents a C₁ to C₈ alkyl group and R² represents hydrogen or a C₁ to C₈ alkyl group. Advantageously the total number of carbon atoms in the comonomer is 5 to 8, and the comonomer is advantageously isoprene. Advantageously, the copolymer contains at least 10% by weight of units derived from butadiene.

In general, the crystallizable block or blocks will be the hydrogenation product of the unit resulting from predominantly 1,4- or end-to-end polymerization of butadiene, while the non-crystallizable block or blocks will be the hydrogenation product of the unit resulting from 1,2-polymerization of butadiene or from 1,4-polymerization of an alkyl-substituted butadiene.

(F) A polyoxyalkylene compound. Examples are polyoxyalkylene esters, ethers, ester/ethers and mixtures thereof, particularly those containing at least one, preferably at least two, C₁₀ to C₃₀ linear alkyl groups and a polyoxyalkylene glycol group of molecular weight up to 5,000, preferably 200 to 5,000, the alkyl group in said polyoxyalkylene glycol containing from 1 to 4 carbon atoms. These materials form the subject of EP-A-0 061 895. Other such additives are described in U.S. Pat. No. 4 491 455.

The preferred esters, ethers or ester/ethers are those of the general formula

    R.sup.31 --O(D)--O--R.sup.32

where R³¹ and R³² may be the same or different and represent

(a) n-alkyl-

(b) n-alkyl-CO-

(c) n-alkyl-O-CO(CH₂)_(x) - or

(d) n-alkyl-O-CO(CH₂)_(x) -CO-

x being, for example, 1 to 30, the alkyl group being linear and containing from 10 to 30 carbon atoms, and D representing the polyalkylene segment of the glycol in which the alkylene group has 1 to 4 carbon atoms, such as a polyoxymethylene, polyoxyethylene or polyoxytrimethylene moiety which is substantially linear; some degree of branching with lower alkyl side chains (such as in polyoxypropylene glycol) may be present but it is preferred that the glycol is substantially linear. D may also contain nitrogen.

Examples of suitable glycols are substantially linear polyethylene glycols (PEG) and polypropylene glycols (PPG) having a molecular weight of from 100 to 5,000, preferably from 200 to 2,000. Esters are preferred and fatty acids containing from 10-30 carbon atoms are useful for reacting with the glycols to form the ester additives, it being preferred to use a C₁₈ --C₂₄ fatty acid, especially behenic acid. The esters may also be prepared by esterifying polyethoxylated fatty acids or polyethoxylated alcohols.

Polyoxyalkylene diesters, diethers, ether/esters and mixtures thereof are suitable as additives, diesters being preferred for use in narrow boiling distillates, when minor amounts of monoethers and monoesters (which are often formed in the manufacturing process) may also be present. It is preferred that a major amount of the dialkyl compound be present. In particular, stearic or behenic diesters of polyethylene glycol, polypropylene glycol or polyethylene/polypropylene glycol mixtures are preferred.

Other examples of polyoxyalkylene compounds are those described in Japanese Patent Publication Nos. 2-51477 and 3-34790, and the esterified alkoxylated amines described in EP-A-1 17,108 and EP-A-326,356.

It is within the scope of the invention to use two or more additional flow improvers advantageously selected from one or more of the different classes A to E outlined above.

The additional flow improver is advantageously employed in a proportion within the range of from 0.01% to 1%, advantageously 0.05% to 0.5%, and preferably from 0.075 to 0.25%, by weight, based on the weight of fuel.

The polymer defined under the first aspect of the invention may also be used in combination with one or more other co-additives such as known in the art, for example the following: detergents, particulate emission reducers, storage stabilizers, antioxidants, corrosion inhibitors, dehazers, demulsifiers, antifoaming agents, cetane improvers, cosolvents, package compatibilizers, and lubricity additives.

The Additive Concentrate (second aspect of the invention)

Additive concentrates according to the invention advantageously contain between 3 and 75%, preferably between 10 and 65%, of the terpolymer in an oil or a solvent miscible with oil.

The concentrate comprising the additive in admixture with a suitable solvent are convenient as a means for incorporating the additive into bulk oil such as distillate fuel, which incorporation may be done by methods known in the art. The concentrates may also contain the other additives as required and preferably contain from 3 to 75 wt %, more preferably 3 to 60 wt %, most preferably 10 to 50 wt % of the additives preferably soluble in oil. Examples of solvent are organic solvents including hydrocarbon solvents, for example petroleum fractions such as naphtha, kerosene, diesel and heater oil; aromatic hydrocarbons such as aromatic fractions, e.g. those sold under the `SOLVESSO` tradename; alcohols and/or esters; and paraffinic hydrocarbons such as hexane and pentane and isoparaffins. The solvent must, of course, be selected having regard to its compatibility with the additive and with the oil.

The Oil Composition (third aspect of the invention)

The oil, preferably fuel oil, composition of the invention advantageously contains a polymer of the invention in a proportion of 0.0005% to 1%, advantageously 0.001 to 0.1%, and preferably 0.01 to 0.06% by weight, based on the weight of oil.

In the oil-containing compositions of the invention, the oil may be a crude oil, i.e. oil obtained directly from drilling and before refining.

The oil may be a lubricating oil, which may be an animal, vegetable or mineral oil, such, for example, as petroleum oil fractions ranging from naphthas or spindle oil to SAE 30, 40 or 50 lubricating oil grades, castor oil, fish oils or oxidized mineral oil. Such an oil may contain additives depending on its intended use; examples are viscosity index improvers such as ethylene-propylene copolymers, succinic acid based dispersants, metal containing dispersant additives and zinc dialkyldithiophosphate antiwear additives. The terpolymer of this invention may be suitable for use in lubricating oils as a flow improver, pour point depressant or dewaxing aid.

The oil may preferably be a fuel oil, e.g., a petroleum-based fuel oil, especially a middle distillate fuel oil. Such distillate fuel oils generally boil within the range of from 110° C. to 500° C., e.g. 150° C. to 400° C. The fuel oil may comprise atmospheric distillate or vacuum distillate, cracked gas oil, or a blend in any proportion of straight run and thermally and/or catalytically cracked distillates. The most common petroleum distillate fuels are kerosene, jet fuels, diesel fuels, heating oils and heavy fuel oils. The heating oil may be a straight atmospheric distillate, or it may contain minor amounts, e.g. up to 35 wt %, of vacuum gas oil or cracked gas oil or of both. The above-mentioned low temperature flow problem is most usually encountered with diesel fuels and with heating oils. The invention is also applicable to vegetable-based fuel oils, for example rape seed oil, used alone or in admixture with a petroleum distillate oil.

The additive composition or concentrate composition useful under the third aspect is that defined in relation to the first or second aspect.

The following Examples, in which all parts and percentages are by weight, and number average molecular weights (Mn) are measured by gel permeation chromatography with polystyrene as standard, illustrate the invention.

EXAMPLES PREPARATION OF POLYMER

Example 1

A number of different polymers were prepared according to the procedure given below for Polymer C, except that the temperature was varied as set out in Table 1 below and the proportions of monomers were also varied to give polymers with the characteristics also as set out in Table 1. The cold filter plugging point (CFPP) results obtained in use of these polymers in two fuel oils are also shown in Table 1.

Preparation of Polymer C

A 3 litre autoclave was charged with 782 ml (610 g) cyclohexane, 249.2 ml (219.3 g) vinyl 2-ethylhexanoate (V2EH) and 63.9 ml (59.4 g) vinyl acetate (VAC). The vessel was pressurised to 9.7 MPa with ethylene and the temperature of the solution raised to 90° C., this pressure and temperature being maintained throughout the reaction. A mixture of 249.2 ml vinyl 2-ethylhexanoate and 39.8 ml vinyl acetate was injected into the autoclave over 75 minutes, as were 17.7 ml t-butyl per-2-ethylhexanoate dissolved in 58.2 ml cyclohexane. The vessel was heat soaked for 10 minutes at 90° C. at the end of the injection, and the reaction mixture drained from the autoclave. Unreacted monomers and solvents were removed by vacuum distillation, and the polymer recovered.

For the preparation of polymers A, D, E, H, J, K, L, M, N and P the initiator t-butyl peroxy pivalate was used instead of t-butyl per-2-ethylhexanoate.

Example 2

In a different set of experiments a further polymer of the invention (polymer P) was tested alongside comparative polymer Cl in Fuels 1 and 2. The results are shown in Table 2.

                                      TABLE 1                                      __________________________________________________________________________     Polymer Performance                 Polymer Characteristics                                                    Overall                                                                            Polymer                                                                            (i)  (ii)                                                                               (iii)                         Polymer                                                                              Fuel 1       Fuel 2       Total                                                                              Temp.                                                                              VA   V2EH                                                                               V total                                                                             (iv)                                                                              (v)                   Designation                                                                          300 vppm                                                                            400 vppm                                                                            Sum                                                                               350 vppm                                                                            450 vppm                                                                            Sum                                                                               Sum (° C.)                                                                      mol %                                                                               mol %                                                                              mol %                                                                               Mn Branching             __________________________________________________________________________     A     -15  -18  -33                                                                               -10.5                                                                               -14  -24.5                                                                             -57.5                                                                              100 3.42 10.4                                                                               13.82                                                                               4378                                                                              2.79                  B     -15  -17.5                                                                               -32.5                                                                             -8.5 -12.5                                                                               -21                                                                               -53.5                                                                              100 3.3  10.73                                                                              14.03                                                                               4737                                                                              3.06                  C     -15  -17  -32                                                                               -9.5 -11.5                                                                               -21                                                                               -53  90 3.8  10.18                                                                              13.98                                                                               4199                                                                              2.76                  D     -14.5                                                                               -17  -31.5                                                                             -8.5 -12  -20.5                                                                             -52 100 3.41 11.3                                                                               14.71                                                                               4907                                                                              3.00                  E     -13.5                                                                               -18  -31.5                                                                             -7.5 -12  -19.5                                                                             -51  90 4.05 12.84                                                                              16.89                                                                               5993                                                                              2.26                  F     -14.5                                                                               -17  -31.5                                                                             -7   -10.5                                                                               -17.5                                                                             -49 100 3.47 10.41                                                                              13.88                                                                               4940                                                                              3.05                  G     -15  -17.5                                                                               -32.5                                                                             -6   -9   -15                                                                               -47.5                                                                              100 3.1  10.9                                                                               14   4451                                                                              2.85                  H     -13.5                                                                               -17  -30.5                                                                             -6.5 -10.5                                                                               -17                                                                               -47.5                                                                              100 3.04 11.12                                                                              14.16                                                                               4604                                                                              2.97                  I     -16  -17  -33                                                                               -5.5 -7.5 -13                                                                               -46 100 4.11 10.78                                                                              14.89                                                                               4231                                                                              2.77                  J     -13  -16.5                                                                               -29.5                                                                             -5.5 -10.5                                                                               -16                                                                               -45.5                                                                              100 4.14 11.84                                                                              15.98                                                                               5609                                                                              3.02                  K     -11  -18.5                                                                               -29.5                                                                             -7   -8   -15                                                                               -44.5                                                                              100 2.89 10.03                                                                              12.92                                                                               4683                                                                              3.43                  L     -14  -18.5                                                                               -32.5                                                                             -4   -7   -11                                                                               -43.5                                                                              100 3.86 14.07                                                                              17.93                                                                               5636                                                                              2.92                  M     -11.5                                                                               -18  -29.5                                                                             -6   -8   -14                                                                               -43.5                                                                              100 2.83 10.19                                                                              13.02                                                                               5214                                                                              3.43                  N     -10  -14.5                                                                               -24.5                                                                             -6   -10  -16                                                                               -40.5                                                                              100 2.73 9.55                                                                               12.28                                                                               4389                                                                              3.32                  O     -14  -13.5                                                                               -27.5                                                                             -3.5 -9   -12.5                                                                             -40 105 3.81 13.92                                                                              17.73                                                                               4414                                                                              3.16                  C.sub.1                                                                              -13.5                                                                               -15  -28.5                                                                             -3   -7   -10                                                                               -38.5                                                                              115 5.35 10.33                                                                              15.68                                                                               4696                                                                              4.00                  C.sub.2                                                                              -13  -16.5                                                                               -29.5                                                                             -1.5 -6   -7.5                                                                              -37 100 4.01 12.49                                                                              16.5 3230                                                                              4.04                  C.sub.3                                                                              -12.5                                                                               -15.5                                                                               -28                                                                               -2   -7   -9 -37 115 4.44 11.29                                                                              15.73                                                                               3655                                                                              4.30                  C.sub.4                                                                              -10.5                                                                               -14.5                                                                               -25                                                                               -4.5 -7   -11.5                                                                             -36.5                                                                              105 13.47                                                                               0   13.47                                                                               4319                                                                              3.99                  C.sub.5                                                                              -9.5 -10.5                                                                               -20                                                                               -3   -7.5 -10.5                                                                             -30.5                                                                              100 2.65 8.26                                                                               10.91                                                                               4658                                                                              3.43                  __________________________________________________________________________

                                      TABLE 2                                      __________________________________________________________________________     Polymer Performance                 Polymer Characteristics                                                    Overall                                                                            Polymer                                                                            (i)  (ii)                                                                               (iii)                         Polymer                                                                              Fuel 1       Fuel 2       Total                                                                              Temp.                                                                              VA   V2EH                                                                               V total                                                                             (iv)                                                                              (v)                   Designation                                                                          300 vppm                                                                            400 vppm                                                                            Sum                                                                               350 vppm                                                                            450 vppm                                                                            Sum                                                                               Sum (° C.)                                                                      mol %                                                                               mol %                                                                              mol %                                                                               Mn Branching             __________________________________________________________________________     P     9.5  -14.5                                                                               -24                                                                               -4.5 -8   -12.5                                                                             -36.5                                                                              100 3.13 9.78                                                                               12.91                                                                               5132                                                                              3.13                  C.sub.1                                                                              -10  -15  -25                                                                               -3.5 -5   -8.5                                                                              -33.5                                                                              115 5.35 10.33                                                                              15.68                                                                               4696                                                                              4.00                  __________________________________________________________________________

The CFPP test, which is carried out by the procedure described in detail in "Journal of the Institute of Petroleum", Volume 52, Number 510, June 1966, pp. 173-285, is designed to correlate with the cold flow of a middle distillate in automotive diesels.

In brief, a sample of the oil to be tested (40 ml) is cooled in a bath which is maintained at about -34° C. to give non-linear cooling at about 1 ° C./min. Periodically (at each one degree centigrade starting from above the cloud point), the cooled oil is tested for its ability to flow through a fine screen in a prescribed time period using a test device which is a pipette to whose lower end is attached an inverted funnel which is positioned below the surface of the oil to be tested. Stretched across the mouth of the funnel is a 350 mesh screen having an area defined by a 12 millimetre diameter. The periodic tests are each initiated by applying a vacuum to the upper end of the pipette whereby oil is drawn through the screen up into the pipette to a mark indicating 20 ml of oil. After each successful passage, the oil is returned immediately to the CFPP tube. The test is repeated with each one degree drop in temperature until the oil fails to fill the pipette within 60 seconds, the temperature at which failure occurs being reported as the CFPP temperature.

The characteristics of Fuel 1 and Fuel 2, both middle distillate fuel oils, are shown in Table 3.

                  TABLE 3                                                          ______________________________________                                         Fuel               Fuel 1   Fuel 2                                             ______________________________________                                         Density     g/ml       0.8437   0.8566                                         Cloud Point ° C.                                                                               -6       +1                                             CFPP        ° C.                                                                               -6.5     -2                                             WAT         ° C.                                                                               -9.41    -3.4                                           % Wax @ 5° C.                                                                       %          1.88     2.31                                           below WAT                                                                      % Wax @ 10° C.                                                                      %          3.12     3.81                                           below WAT                                                                      Distallation (D86)                                                             IBR         ° C.                                                                               180      197                                            10                     225      255                                            20                     244      269                                            30                     261      282                                            40                     274      293                                            50                     285      303                                            60                     295      314                                            70                     307      326                                            80                     319      338                                            90                     335      352                                            95                     347      362                                            FBP                    358      367                                            FBP-90                 23       15                                             90-20                  91       83                                             ______________________________________                                    

As can be seen from Tables 1 and 2, polymers A to P inclusive, having all the features (i) to (v) as specified under the first aspect of the invention, showed improved performance over comparative polymers (C₁ to C₅) lacking one or more of the features (i) to (v), when comparing the overall sum of CFPP results observed in the two test fuels. As individual fuels can differ somewhat in their response to particular additives at any given treat rate (a fact well known to the skilled person in this field), summed comparisons over a single set of tests which take into account a multiplicity of fuels and treat rates provide a more accurate overall assessment of the potency of a particular polymer.

Furthermore, Table 1 illustrates that the polymers having the preferred ranges for features (i), (ii), (iii) and (v) as hereinbefore defined (polymers A to H inclusive) gave the best overall CFPP performance, further indicating the improved compositions that may be obtained through control of the features (i) to (v). 

What is claimed is:
 1. An additive composition comprising an oil soluble ethylene polymer comprising, in addition to units derived from ethylene, units of the formula: ##STR7## and units of the formula: ##STR8## wherein each R¹ and R² group independently represents hydrogen or methyl; each R³ group independently represents an alkyl group having between 1 and 4 carbon atoms; each R⁴ group independently represents a branched chain alkyl group having up to 15 carbon atoms and different from R³ ;characterised in that: (i) the mole percentage of units (I) in the polymer is in the range of 2.5 to 4.5%, (ii) the mole percentage of units (II) in the polymer is in the range of 9.5 to 14%, (iii) the total mole percentage of units (I) and units (II) in the polymer is in the range of 12 to 18%, (iv) the number average molecular weight (Mn) of the polymer is in the range of 3500 to 6000; and (v) the degree of branching of the polymer is in the range of 2.2 to 3.6 methyl groups per 100 methylene units, as measured by proton NMR and corrected for the number of methyl and methylene groups in R³ and R⁴ groups.
 2. The composition of claim 1 wherein R⁴ represents a branched chain alkyl group having 8 to 15 carbon atoms other than a tertiary alkyl group.
 3. The composition of claim 1, wherein R⁴ represents a branched chain alkyl having at most seven carbon atoms.
 4. The composition of claim 3 wherein(i) is in the range of 3 to 4.1, (ii) is in the range of 10.1 to 13, (iii) is in the range of 13.8 to 17, and (v) is in the range of 2.2 to 3.4.
 5. The composition of claim 4, wherein R¹ and R² are hydrogen.
 6. The composition of claim 5, wherein R³ is methyl or ethyl. R⁴ is 1-ethyl pentyl.
 7. The composition of claim 1, wherein R⁴ is 1-ethyl pentyl.
 8. A method for improving the low temperature properties of an oil, comprising admixing the oil with the composition of claim
 7. 9. The method of claim 8, wherein the oil is a fuel oil having a wax content of from 3.0 to 4.5% by weight.
 10. A polymer as defined in claim
 7. 11. An additive concentrate composition comprising the additive of claim and a mutually-compatible solvent therefor.
 12. An oil composition comprising an oil and a minor amount of the composition of claim
 1. 13. A polymer as defined in claim
 1. 14. A method for improving the low temperature properties of an oil, comprising admixing the oil with the polymer of claim
 13. 15. A method for improving the low temperature properties of an oil, comprising admixing the oil with the composition of claim
 1. 16. The method of claim 15, wherein the oil is a fuel oil having a wax content of from 3.0 to 4.5% by weight. 